No abstract

The main goal of this study is to investigate the evaporation process of a coolant (water droplets) which is injected through spray nozzles mounted on a steam turbine bypass pipeline in a co-generator system. The study includes several important factors: (1) the effects of four elbows on the flow pattern and evaporation process of the water particles, (2) heat transfer that affects the steam temperature and also the evaporation rates, and (3) the effects of inserting a perforated plate on the flow pattern and evaporation process. The first goal of this study is to investigate whether or not the existence of elbows in the pipeline will enhance the evaporation process of water droplets. Two effects have been observed so far. One is that the generation of turbulence increases in the core of the elbow which results in a higher heat transfer rate between particles and steam and the other is that particles are forced to impinge onto the outer side of the pipe wall in the elbow due to the centrifugal inertia force of the flow in the curvature path. The second goal is to carefully study the heat transfer effects of three different modes; i.e., the heat exchange between the steam and the water particles, the heat transfer of flow to the wall due to turbulence convection, and the conjugate heat transfer by means of heat conduction through the pipe wall and insulation materials. The last goal of the research is to investigate the effect of the insertion of a perforated plate downstream from the cooling water spray nozzles. A detailed analysis was conducted by microscopically modeling the flow through each hole of the perforated plate. Modeling of the high-pressure turbulent steam flow was based on a non-staggered finite volume method in three-dimensional, turbulent, compressible, two-phase dispersed flow formulations. The investigation of the structure of liquid spray jets during the transition into the gaseous phase was accomplished by developing a physical model of a particle tracking technique to investigate evaporation processes of the liquid droplets in a highly turbulent flow. Computations were performed by separating the entire pipeline system into four sections, each of which was generated in a three-dimensional grid system for more efficient computations by maintaining a sufficiently large number of meshes for each section. Flow calculations were made in each region separately by patching the end conditions from one pipe to the inlet conditions of the next one. Through this research, numerous data have been acquired and analyzed for heat transfer mechanisms of the cooling water droplets in the pipeline system. The results of the computations were verified by comparing them with theoretical models, and were shown to be quite reliable.

No abstract

This paper presents a study of the numerical simulations of a steam flow and heat transfer behavior when subjected to a cooling water spray in the pipe downstream from a high-pressure turbine bypass valve. The structure of a cooling water spray injected into a steam flow was studied for the purpose of developing a physical model to investigate the dissipation and evaporation processes of the cooling water droplets in a high temperature, high turbulent steam flow passage. Heat transfer rates were calculated for a better understanding of the temperature variations in the entire system. A dispersed two-phase model was incorporated for the particle tracking of the droplets injected into the steam flow and the water evaporation process was observed. Further, this study was continued by installing a perforated plate in the pipe section downstream from the water cooling injections. The results of the calculations are quite reasonable, and show a physically sound state.

The main goal of this study is to investigate the evaporation process of a coolant (water droplets) which is injected through spray nozzles mounted on a steam turbine bypass pipeline in a co-generator system. The study includes several important factors: (1) the effects of elbows on the flow pattern and evaporation process of the water particles; (2) heat transfer that affects the steam temperature and also the evaporation rates; and (3) the effects of insertion of a perforated plate in the flow path on the evaporation process. Modeling of the high-pressure turbulent steam flow was based on a non-staggered finite volume method in 3-D, turbulent, compressible, two-phase dispersed flow formulations. Computations were performed by separating the entire pipeline system into four sections, each of which was generated in a 3-D grid system for more efficient computations by maintaining a sufficiently large number of meshes for each section. Flow calculations were made in each region separately by patching the end conditions from one pipe to the inlet conditions of the next one. Through this research, numerous data have been acquired and analyzed for heat transfer mechanisms of the cooling water droplets in the pipeline system. The accuracy of the computations were validated by comparing them with theoretical models, and were shown to be quite reliable.